Properties of Hydroprocessed Base Oils

ABSTRACT

Solvent extraction is applied to a hydrotreated base oil to create at least one higher quality product stream and at least one lower quality product stream, wherein the at least one higher quality product stream includes an improvement over the hydrotreated base oil in at least one of viscosity index, low temperature properties, volatility, and oxidation stability relative to that of the feedstock.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. Pat. No.9,862,894, formerly co-pending application Ser. No. 15/212,180, filedJul. 15, 2016, and issued on Jan. 9, 2018, which is a continuationapplication of U.S. Pat. No. 9,394,495, formerly co-pending patentapplication Ser. No. 14/488,926, filed on Sep. 17, 2014, and issued onJul. 19, 2016, which claims the benefit of Provisional Application No.61/879,409, filed Sep. 18, 2013; and this application claims the benefitof U.S. Provisional Application Nos. 62/514,639 and 62/519,149, filedJun. 2, 2017, and Jun. 13, 2017, respectively; and U.S. Pat. No.9,862,894 claims the benefit of U.S. Provisional Application No.62/349,441, filed Jun. 13, 2016, all of which applications and patentsare hereby incorporated herein by reference, in their entirety.

TECHNICAL FIELD

The present disclosure relates to further processing of hydroprocessedbase oils through subsequent solvent treatment to create improvedproperties, and more particularly improved low temperature properties,viscosity index, oxidation stability, and volatility properties.

BACKGROUND

Finished lubricants include two general components, lubricating basestocks and additives. Base stocks are made by producers, which may berefiners which make base stocks from crude oil, or re-refiners whichmake base stocks from used lubricating oils. Lubricating base stock isthe major constituent in these finished lubricants and contributessignificantly to the properties of the finished lubricant. In general, afew lubricating base stocks are used to manufacture a wide variety offinished lubricants by varying the mixtures of individual lubricatingbase stocks and individual additives. While finished lubricants may beused, for example, in automobiles, diesel engines, axles, transmissions,and a wide variety of industrial applications, motor oil in crankcasesof cars and trucks is the largest volume single market for finishedlubricants.

A base oil is created by blending two or more base stocks together andit is thus generally base oils (e.g. the blended base stocks) which areused to make the finished lubricants. Base oils typically comprise over70% of the finished lubricant and additives make up the balance.Additives are blended with the selected base oil blend to provide afinished lubricant composition as intended to improve (or “correct”)select properties of the finished lubricants. Typical additives include,for example, pour point depressants, anti-wear additives, extremepressure (EP) agents, detergents, dispersants, antioxidants, viscosityindex improvers, viscosity modifiers, friction modifiers,de-emulsifiers, antifoaming agents, corrosion inhibitors, rustinhibitors, seal swell agents, emulsifiers, wetting agents, lubricityimprovers, metal deactivators, gelling agents, tackiness agents,bactericides, fungicides, fluid-loss additives, colorants, and the like.

In making finished lubricants, motor oil manufacturers blend base oilsand additives to formulate products that meet the finished lubricantspecification. Manufacturers seek to minimize use of expensive additive(“correction”) fluids that are otherwise required to compensate for anyshortfall in the base oil. Viscosity Index (VI) is a measure of thedegree to which the viscosity of a base oil changes over changes intemperature. Less change is better, and less change correlates to ahigher VI number. Viscosity Index Improvers (referred to as VIImprovers) are widely used in making motor oils, serving to maintain ahigher thickness of the oil at higher temperatures than would otherwisebe the case. However, VI improvers are not only expensive but theyincrease lubricant viscosity, thus making it more difficult to achievelow cold cranking viscosities. It is thus advantageous to use base oilsof higher VIs (before adding VI Improvers), since this both minimizesadditive cost and reduces the amount of correction fluid needed toachieve the cold cranking specification, which requires thinner baseoils in the 0 W and 5 W motor oil grades. Base oils able to be blendedinto finished lubricants that achieve the 0 W and 5 W motor oil graderequirements generally require a viscosity level of no greater than 120SUS (at 100° F.) or alternatively measured 4.5 centistokes (at 100° C.).At such low viscosity levels the volatility specification of 15% or 13%typically can only be achieved in Group III base oils. Thus, motor oilmanufacturers seek base oils with higher VIs and excellent lowtemperature properties, and additionally low volatility.

Finished lubricants must meet the specifications for their intendedapplication as defined typically by the concerned governingorganization, although increasingly many equipment manufacturers arecreating their own specifications. Motor oil specifications in theUnited States are set by the International Lubricant Standardization andApproval Committee (ILSAC), a tri-partite group of original equipmentmanufacturers or OEMs (car and truck manufacturers), additive companies,and base oil producers. ILSAC will periodically issue revised standardsfor motor oils which are termed GF (for Gasoline Fuel) and are followedby a number, that number currently being 5, and the current GF-5standards became effective on Oct. 1, 2011.

Among other requirements, GF-5 stipulates that motor oils must meet thespecifications defined in SAE J300 (established by the Society ofAutomotive Engineers) for 0 W, 5 W, 10 W, and higher multi-grade oils,which include tests for cold cranking viscosity at very lowtemperatures. The “W” in the grade designations stands for Winter and itdefines the cold temperature requirements of the motor oil grade. Lowtemperature performance is critical for engine oils because of coldtemperature conditions that engines are exposed to prior to start-up invarious cold climates. A lube oil base stock that provides improved lowtemperature performance could allow inclusion of lower quality, lessexpensive co-base stocks or a reduction in the amount of viscositymodifier or pour point depressant in the engine oil formulation.

A key measure of low temperature performance is measured by thelow-temperature cranking viscosity (cold crank viscosity) as is definedin test method D-5293 (“D” in the test method identifier denotes itsapproval as an ASTM test method). This test method is abbreviated as CCS(for Cold Crank Simulator) and it is conducted at different temperaturesfor each grade of lube oil. Column 2 in Table 1 in SAE J300 (copiedbelow) shows the Low-Temperature Cranking Viscosity (measured in mPa-s)requirements for grades of motor oil, the most restrictive of which arefound on the first two rows, 0 W and 5 W. The third column shows the LowTemperature Pumping Viscosity (often referred to as the mini-rotaryviscometer test, or MRV test, and measured as per D-4684).

TABLE 1 SAE viscosity grades for engine oils⁽¹⁾⁽²⁾ Caution: kinematicviscosity ranges for SAE 8 to SAE 20 viscosity grades partially overlap.How to assign a single viscosity grade to an engine oil satisfying thekinematic viscosity specifications of more than one grade is covered inSection 6 of this document. Low-Temperature Low-Temperature (° C.)Low-Shear-Rate Low-Shear-Rate (° C.) Pumping Kinematic KinematicHigh-Shear-Rate SAE Cranking Viscosity⁽⁴⁾ mPa · s Viscosity⁽⁵⁾ (mm²/s)Viscosity⁽⁶⁾ (mm²/s) Viscosity⁽⁶⁾ (mPa · s) Viscosity Viscosity⁽³⁾, mPa· s Max with at 100° C. at 100° C. at 150° C. Grade Max No YieldStress⁽⁴⁾ Min Max Min  0 W 6200 at −35 60 000 at −40 3.8 — —  5 W 6600at −30 60 000 at −35 3.8 — — 10 W 7000 at −25 60 000 at −30 4.1 — — 15 W7000 at −20 60 000 at −25 5.6 — — 20 W 9500 at −15 60 000 at −20 5.6 — —25 W 13 000 at −10 60 000 at −15 9.3 —  8 — — 4.0 <6.1 1.7 12 — — 5.0<7.1 2.0 16 — — 6.1 <8.2 2.3 20 — — 8.9 <9.3 2.8 30 — — 9.3 <12.5 2.9 40— — 12.5 <16.3 3.5 (0 W-40, 5 W-40, and 10 W-40 grades) 40 — — 12.5<16.3 3.7 (15 W-40, 20 W-40, 25 W-40, 40 grades) 50 — — 16.3 <21.9 3.760 — — 21.9 <28.1 3.7 ⁽¹⁾Notes - 1 mPa · s = 1 cP; 1 mm²/s = 1 cSt⁽²⁾All values, with the exception of the low-temperature crankingviscosity, are critical specifications as defined by ASTM D3244 (seetext, Section7.) ⁽³⁾ASTM D5293: Cranking viscosity - The non-criticalspecification protocol in ASTM D3244 shall be applied with a P value of0.95. ⁽⁴⁾ASTM D4684: Note that the presence of any yield stressdetectable by this method constitutes a failure regardless of viscosity.⁽⁵⁾ASTM D445 ⁽⁶⁾ASTM D4683, ASTM D4741, ASTM D5481, or CEC L-36-90.

In the above table, motor oils that achieve below 6,200 mPa-s at −35degrees centigrade (C) will meet the cold cranking requirement for 0 W,whereas motor oils that are above 6,200 mPa-s but less than 6,600 mPa-swill meet the cold cranking requirement for 5 W motor oils. Thinner oils(that is, lower in viscosity) are needed to achieve improved (lower)cold cranking viscosities. As is shown in the third column of Table 1above, the low temperature pumping viscosity MRV test is applied attemperatures ranging from −15 C down to −40 C and in this test any showof stress will constitute a failure.

The core challenge in meeting these low temperature tests is that evenas thinner oils tend to have improved low temperature properties,thinner oils are also typically more volatile, and volatility isrestricted in GF-5 to 15% or below as measured by D-5800 (also referredto as NOACK). In the case of DEXOS™, which is General Motors'specification, the motor oil must not exceed a NOACK volatility of 13%.Most particularly, in the lightest motor oil grades (0 W and 5 W), it isdifficult if not impossible to economically achieve both a low coldcrank viscosity and comply with the 15% (or 13% in a DEXOS™specification) volatility specification without using base stocks havinghigher VIs. Thus lower CCS values and lower volatility fight each otherbut are addressable in the lightest viscosity motor oil grades by use ofbase oils with higher VIs. Higher viscosity grades (that is thickeroils) have less difficulty achieving both their cold cranking levels andthe volatility specification since heavier base oils are inherently farless volatile than lighter base oils and the cold cranking viscositylevel is higher (e.g. less stringent).

In addition to cold cranking viscosity, finished lubricant manufacturersalso evaluate other important low temperature characteristics such aspour point (preferably measured as per D-97) and cloud point (preferablymeasured as per D-2500). An additional low temperature test method isthe Brookfield Viscometer Test which measures low temperature viscosity(preferably measured as per D-2983, or “Brookfield Viscosity”) and isapplied to qualify Automatic Transmission Fluids (ATF's) and hydraulicfluids. Cold cranking viscosity, Brookfield Viscometer Test, MRV test,pour point, and cloud point are referred to herein as comprising “lowtemperature properties”. In each of these instances, a lower numberdenotes a higher performance level. As examples, a cold crankingviscosity of 3,500 is better than 4,000, a pour point of −15° C. isbetter than −10° C., and a cloud point of −5° C. is better than 0° C.

Finished lubricant standards are becoming increasingly challenging tomeet in response to continually evolving and increasingly demandingmarket applications. Whereas historically higher lubricant standards inthe earlier years were achieved through better additives, in the 1990sand thereafter higher base oil quality has increasingly been required tomeet the higher finished lubricant standards. Most notably, increasinglystringent finished lubricant standards in motor oils now increasinglyrequire base oils with excellent low temperature properties (includinglower viscosity thus achieving better fuel economy), lower volatility(thus achieving lower emissions) and higher oxidation stability (thuslasting longer in use).

Oxidation stability is a further important property of base oils (and inthe finished lubricants) as a major goal is to maximize useful life ofthe lubricant, thus delaying a need for its replacement in theapplication. Not only does a longer lubricant life represent costsavings from less frequent changes, but it also indicates a higheraverage level of performance versus time, thus providing betterlubrication even while a lubricant is being degraded during use.Therefore oil stability and durability (as indicated by oxidationstability) is of particular importance in evaluation of base oils and inthe finished lubricants made from base oils. Oxidation stability, andits associated elements of sludge, deposit and viscosity control, applyin making passenger car motor oil (PCMO), Heavy Duty Engine Oils(HDEOs), and many industrial lubricants.

Oxidation stability is defined and measured in numerous tests based onthe specific market application of the lubricant. Such tests definestandards in base oils or finished lubricants and may be established byequipment manufacturers or by third party organizations. In the GF-5requirements created by ILSAC which took effect in October 2011 and areapplied to PCMOs, no less than 6 (of about 21) tests are directedtowards measuring different aspects of oil stability. These testsinclude: 1. Wear and Oil Thickening (D-7320), 2. Wear, Sludge, andVarnish Test (D-6593), 3. High Temperature Deposits, TEOST MHT (D-7097),4. High Temperature Deposits TEOST 33C (D-6335), and 5. Aged Oil LowTemperature Viscosity, ROBO Test (D-7528) or 6. Aged Oil Temperature LowTemperature Viscosity (D-7320).

In industrial applications, such as in the manufacturing of HydraulicFluids, Turbine Oils, Compressor Oils, and Industrial Gear Oils,oxidation stability is also measured in many other tests including;Determination of Oxidation Stability of Straight Mineral Oils (IP-306),Test of Susceptibility of Ageing According to Baader (DIN 51554),Oxidation Characteristics of Inhibited Mineral Oils (D-943),Determination of the Sludging and Corrosion Tendencies of InhibitedMineral Oils (D-4310), Oxidation Stability of Steam Turbine Oils byRotating Pressure Vessel Oxidation Test (RPVOT), (D-2272), Determinationof oxidation stability and insolubles formation of uninhibited turbineoils at 120° C. without the inclusion of water (Dry TOST Method)(D-7873), Determination of Oxidation Stability of Inhibited MineralTurbine Oils (IP-280), 3462 Panel Coker Test (FTM 791A), Standard TestMethod for Corrosiveness and Oxidation Stability of Hydraulic Oils,Aircraft Turbine Engine Lubricants and Other Highly Refined Oils(D-4636), Pneurop Oxidation (DIN 51352), Standard Test Method forThermal Stability of Hydraulic Oils (D-2070), Hydrolytic Stability ofHydraulic Fluids (Beverage Bottle Method) (D-2619), and OxidationCharacteristics of Extreme Pressure Lubricating Oils (D-2893), amongothers. The ability to meet the standards of these oxidation tests oftenrequires using higher quality base oils.

The American Petroleum Institute (API) has classified base oil byquality into groups, with mineral oils constituting Groups I, II andIII, and other non-mineral derived oils constituting Groups IV and V(Group VI is a European classification). In API's classification system,higher quality is designated by a higher number. Thus Group III ishigher quality than Group II and Group II is higher quality than GroupI. In general, Group II lube base stocks have much poorer CCS-volatilityrelationships relative to Group III and Group IV base stocks.

TABLE 2 API Base Oil Group Classifications Viscosity Group IndexSaturates and Sulfur Other I 80-120 <90% and/or >=0.03% II 80-120 >=90%and <0.03% III ≥120 >=90% and <0.03% IV PAO Poly Alpha Olefin V PolyEsters (others) VI Europe Only (ATIEL) PIO (Poly Internal Olefins)

The API Base Oil Group classification system defines base oil quality bythree criteria: 1) sulfur content (preferably low to reduce harmfulemissions), 2) saturates (to improve oxidation stability, reduce sludgeand deposit formation, and achieve better VIs and lower volatilities),and 3) viscosity index (VI) (the higher, the better). As noted above, VImeasures the rate of change in viscosity in response to change intemperature. VI is a calculated number relative to reference base oilsbased on the measurement of viscosity at two temperatures, 40° C. and100° C. A higher VI indicates less viscosity change in response totemperature change, and thus higher quality base oil. Saturates ingeneral (which include both paraffinic and naphthenic compounds, whichare also referred to as cyclo-paraffinic compounds) are well known tohave a smaller change in viscosity in response to temperature comparedwith aromatics and polar compounds, and thus have higher VIs. It is thuswell known that a higher level of saturates in base oil increasesquality as the more saturated base oils achieve higher VIs, althoughthere are distinctions even with the saturates category as noted next.

Within the saturates category of compounds, paraffinic compounds areknown to have higher VIs than naphthenic components. While paraffiniccomponents are known to have a higher VI than naphthenic compounds,naphthenic compounds are known to have better low temperature propertiesthan paraffinic oils. Whereas VI is calculated based on viscositymeasurements at 40° C. and 100° C., in contrast (and as noted in Table 1above) calculation of cold cranking viscosity is measured at −35° C.,−30° C., and −25° C., for the grades of 0 W, 5 W and 10 W, respectively.The CCS temperatures of −35° C., −30° C., and −25° C. are each far belowthe 40 C (lowest) temperature used for determining VI. It is thusevident that, while both VI and cold crank measure viscosities of oil,the temperature ranges covered by these two test methods are vastlydifferent, spanning a huge range from 100° C. on down to −35° C. This isa difference of 135° C. (243° F.). The combination of the twospecifications, VI and cold crank, highlights a fundamental challengefor motor oils; they are required to operate across a very broadtemperature range, in both very high temperature and very lowtemperature environments. This is appropriate since engine oils, oncemanufactured, may be sold and used anywhere in any season, but they mustalways protect the engine in all operating environments.

The latest performance standards established by ILSAC (GF-5) arespecified tests which focus on ensuring the finished lubricant (which isthe base oil and additives together in combination) will achieve certainexplicit measures of fuel efficiency, catalyst compatibility, minimumlevels of wear and deposits, and, of notable importance in the lighterlubricant viscosity range, a limitation on volatility. Over the years,the increased GF standards have translated into enormous pressure onboth virgin base oil producers and additive manufacturers to improvetheir products by creating higher quality base oils and higherperformance additive packages to create higher quality motor and engineoils. For base oils today, this means increased demand for higherquality Group II base oils and, in many cases, Group III base oils. Thisever upward quality trend has continued for many years and virgin baseoil producers have been forced to upgrade their facilities to producehigher quality base oils to meet the more stringent emissions and fueleconomy standards. Most of the smaller, less efficient refineriesproducing only Group I virgin base oil could not justify the capitalupgrades and either shut down their base oil plants within the refinery,or shut down the entire refinery. Understanding the historical evolutionof the technologies for making base oils is helpful to place in contextthe novelty of the present invention.

To make base oils from crude oil (called virgin base oils), first crudeoil is distilled in an atmospheric column and then the bottoms from theatmospheric column pass to a vacuum column, in which a distillate calledVacuum Gas Oil (or VGO) is created. In certain instances the residualfrom the vacuum column may be processed in a solvent de-asphalting unitto create de-asphalted oil (or DAO). As shown in FIG. 1 (Sourced fromSolomon Associates, as reported in Lubes N′ Greases Magazine, March2016, page 34), the distillate or DAO is then processed by one of threedifferent pathways to make Group I, II or III base oils. The firstpathway (box 100 in FIG. 1) starts with solvent extraction and then theraffinate produced from solvent extraction is further processed bysolvent de-waxing and hydrofinishing to create Group I base oils (thelowest quality). This was the first technology upgrade and generallybegan in the 1960s when hydrotreating was first applied to base oils,which was about 30 years after solvent extraction was first introducedin the 1930s. Exxon-Mobil introduced an innovation on the existing GroupI base oil process which inserted hydrocracking or hydrotreatingcapability after solvent extraction and before the wax treatment stepand these are the two smaller boxes called Raffinate Hydrocracking orRaffinate Hydrotreating which are then followed by the solvent orcatalytic dewaxing steps. Exxon's approach enables Group II and GroupIII base oils to be created by upgrading the raffinate produced in theinitial solvent extraction step (which was applied to the VGO or DAOfeedstock).

The next innovations crude oil refiners developed were hydroprocessingtechnologies such as hydrocracking, hydrotreatment, hydrofinishing,catalytic de-waxing, and iso-dewaxing, and these are shown in dashedboxes 130 and 160 in FIG. 1. As used herein, the term “hydroprocessing”is used to refer to hydrocracking, hydrotreatment, hydrofinishing,catalytic de-waxing, and iso-dewaxing as well as any associatedtechnologies which apply hydrogen and catalysts under conditions oftemperature, pressure, and residence times to achieve improvement in thefeedstock. Box 130 in FIG. 1 originates with a Fuels Hydrocracker (e.g.targeted for making gasoline, diesel, jet fuel and the like) whereas box160 originates with a Lube Hydrocracker (e.g. targeted for making lubeoils). As shown each of these two pathways will make higher qualityGroup II and Group III base oils. The advanced hydroprocessingtechnologies shown in boxes 130 and 160 are now the dominant processesused for making base oils, substantially displacing the traditionalsolvent extraction-solvent de-waxing-hydrofinishing processing route tobase oil production shown in the upper large box. Exxon has continued toproduce using its Raffinate Hydroprocessing technologies with somesuccess as well.

While most lube base oil is made from crude oil, it is well known thatused lubricating oil is an excellent feedstock for re-refining into baseoil (which are then called re-refined base oils). FIG. 2 shows themultiple pathways to creating base oils from used lubricating oils. Asthe first step re-refining technologies most commonly apply vacuumdistillation (200), thermal de-asphalting (230), or solventde-asphalting (260), which create one or more intermediate liquids,certain of which are then further upgraded to create marketable baseoil, most commonly either by clay treatment, solvent extraction, orhydrotreatment. (In the 1960s, acid/clay treating was prevalent but wasdiscontinued due to extensive by-product solids creation that becameground pollutants, creating many super-fund sites that incurred massiveclean-up costs.)

Re-refining has now evolved from the 1960s to where use of hydrotreatingand to a lesser extent solvent extraction have become preferredprocessing technologies as the second step following vacuumdistillation, thermal deasphalting or solvent de-asphalting. In the vastmajority of all re-refining technologies, prior to the hydrotreatingstep or the solvent extraction step, atmospheric and vacuum distillationis utilized to remove both light ends and asphaltenes. The reason vacuumdistillation is preferred is that thermal de-asphalting will createcracking which degrades the quality of the intermediate liquid. Solventde-asphalting creates DAO, and DAO is a poor feedstock and the processleaves behind much of the valuable base oil fraction, thus creating pooryields. When vacuum distillation is used to create the intermediateliquid in a re-refinery, the distillate (charged to the clay treater,hydrotreater or solvent extraction unit) is called a vacuum gas oil(VGO). Although still produced in far lower quantities than virgin baseoils, use of re-refined base oils made by hydrotreating of VGO hasdramatically increased in recent years as the quality of the used motoroil pool has increased dramatically with higher lubricant standards,thus resulting in higher quality re-refined base oils. Because of theincreased quality of the used lubricating oil feedstock today, it is nowpossible to use hydrotreating of VGO made from used lubricating oils tomake excellent quality Group II+(with a VI of 115 to 119) and even GroupIII base oils, in part by being selective about sourcing feedstocks.

While hydrotreatment of VGO made from used lubricating oils can achievehigh quality base oils, technically it is also possible to use solventextraction of VGO made from used lubricating oils to even make Group IIIbase oils. However, as the final step in making re-refined base oilssolvent extraction suffers from three large challenges. Firstly, thesulfur level of the primary base oil is usually in the range of 200 to300 ppm or more, which although it falls within the Group IIspecification, is still high compared with hydrotreated base oils.Secondly, the color of the base oil is often yellow versus the almostclear base oils typically produced by hydrotreating. Thirdly, theextract by-product created from solvent extraction of VGO is notsuitable for sale as base oil, and is typically sold as low value fueloil; thus solvent extraction has lower base oil yield.

In U.S. Pat. No. 3,617,476 issued to Woodle in 1971, a process isdisclosed in a sequence involving first applying mild hydrogenation,then followed by solvent refining and dewaxing. The mild hydrogenationconditions includes a pressure not greater than 600 PSIG and the patentnotes a highest VI achieved of 111, thus not even achieving Group II+.Such mild process hydrogenation conditions are not capable of achievingthe advanced levels of de-aromatization, de-sulfurization, andde-nitrification demanded by today's higher quality finished lubricantspecifications, and this is demonstrated partly by the upper VI value of111 reported in Woodle '476. In U.S. Pat. No. 4,085,036 issued to Murphyin 1978, a process is disclosed applying hydro-desulfurization to afeedstock (a lubricating oil fraction created by distillation of crudeoil) containing at least 1.5% sulfur, whereupon the residual portion ofthe distillation is subjected to a de-asphalting step and thede-asphalted oil therefrom is combined with the distillate and thensolvent extracted. The raffinate from the solvent extraction step isthen subjected to de-waxing, followed by one or more finishing stepssuch as hydrofinishing and clay treating. The purpose of Murphy '036process is to remove sulfur more efficiently but the patent makes noclaims to any improvements in either viscosity index or low temperatureproperties.

An alternative process for creating a lubricating oil from the residualof vacuum distillation of an asphaltic crude oil by means of solventtreatment is offered in U.S. Pat. No. 3,414,506 (issued to Compagne in1968). A de-asphalted oil is created by applying a methanol/butanolmixture, which is then further processed by applying hydrotreatment tothe de-asphalted oil. A de-waxing step is noted as an option in betweenthe de-asphalting step and the hydrotreating step. The process creates a44% asphaltic stream and other lower valued streams, and achieves amaximum VI of only 95 in the base oil product with base oil yieldsranging from just 15.5% to 28.5%. While this process does recover baseoil contained in the vacuum residual (which would otherwise be lost mostlikely as fuel oil), the patent does not address what happens to themajority stream, which is the distillate from vacuum distillation (theVGO).

U.S. Pat. No. 3,691,067 issued to Ashton in 1972 describes applyinghydrotreatment to create a series of narrow cut fractions (e.g. liquidshaving a relatively small boiling range of about 200 to 250° F.)tracking the effect of hydrotreatment on improving the VI of eachfraction. While Ashton '067 does not apply solvent extraction to ahydrotreated base oil, a composite product created after hydrotreatingand de-waxing exhibits a VI of 93, which is substantially greater thanthe feedstock VI of 64, and also exhibits a fairly low pour point of−10° F. After hydrotreating but before de-waxing the pour point of thecomposite product was 110° F. and the VI was 113. Thus the de-waxingstep has the beneficial effect of drastically lowering the pour point ofthe product by about 120° F. Ashton '067 also notes how hydrotreatingand dewaxing the distillate increases VI substantially over that of thefeedstock with the heavier fractions increasing their VI dramaticallyhigher than the lighter fractions (68 to 83 versus 90 to 95). It is alsonoted (in Table VII of Ashton) that solvent refining of the charge(which is a heavy raw wax distillate, 80% of which falls in the boilingrange of 880° F. to 975° F.) will improve the VI from 64 to a range of92 to 98 across the fractions. One detriment to the hydrotreating inAshton '067 is using a temperature of 775° F. with a liquid hourly spacevelocity (LHSV) as low as 0.24, which in the example creates a yield ofonly 78.5%, the balance of which is presumably much lighter and lessvaluable hydrocarbons which are outside the lube fraction boiling range.While claim 1 of Ashton states the process conditions of the processwill produce substantially no cracking, the presented process conditionsof Ashton would result in substantial cracking as occurred in the citedexample, and as may be intimated will occur where the processspecifically notes maintaining temperature and space velocity at levelsdesigned to achieve a minimum yield of only 60% (column 3, row 4).

In view of the foregoing, it may be appreciated that there is a growingneed for base oils with excellent low temperature properties, inaddition to higher viscosity indexes and increased oxidation stability,and which also does not result in a materially degraded level ofvolatility.

SUMMARY

According to the present disclosure, it has been found that applicationof solvent treatment to a hydrotreated base oil feedstock yields baseoils with excellent low temperature properties, higher viscosityindexes, improved oxidation stability and without any materialdegradation in volatility. In at least one embodiment of the invention,solvent treatment is applied to a hydroprocessed base oil stream tocreate at least one higher product quality stream exhibiting improvedlow temperature properties. Solvent treatment is preferably applied toseparate the hydroprocessed base oil stream into two different streamswith virtually zero loss of yield in the total (volume or mass) of thetwo product streams in the aggregate as compared with the volume or massof the hydrotreated base oil feed stream (on a solvent free basis).

For ease in presentation (and without limitation), this specificationdescribes two different products created by solvent treatment which arereferred to as higher quality product or lower quality product (orstream). A preferable solvent demonstrated to achieve the notedimprovements is n-methyl-2-pyrollidone and the preferred process usesranges for solvent to oil ratio, temperature, pressure and number ofstages as disclosed herein. Additionally a preferred mode ofimplementing the invention is to combine the solvent recoverydistillation function with a volatility and viscosity control capabilitythereby extending the functionality of the distillation equipmentproviding the solvent recovery capability. The invention is applicableto hydroprocessed base oils that have been made from crude oils (akavirgin base oils) and from used lubricating oils (aka re-refined baseoils).

Block diagrams in which one process of the present invention is appliedto hydroprocessed base oils made from crude oil and used lubricatingoils are shown in FIGS. 3 and 4, respectively. In each instance as thefinal step, solvent treatment is applied to a base oil that was priorcreated by hydroprocessing, most commonly through hydrotreating, butwhich also may be produced by hydrocracking or hydrofinishing (as wellas other hydrogen based technologies). As noted above, and as will beexplained in further detail below, solvent treatment is preferablyfollowed by a fractionation step applied for controlling volatility andenabling creation of products of specific viscosities, with suchfractionation step preferably being integrated into the solvent recoverystep.

The foregoing has outlined broadly the features and technical advantagesof the present invention in order that the detailed description of theinvention that follows may be better understood. Additional features andadvantages of the invention will be described hereinafter which form thesubject of the claims of the invention. It should be appreciated bythose skilled in the art that the conception and the specific embodimentdisclosed may be readily utilized as a basis for modifying or designingother structures for carrying out the same purposes of the presentinvention. It should also be realized by those skilled in the art thatsuch equivalent constructions do not depart from the spirit and scope ofthe invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating three different general pathwaysand seven different general routes for creating base lube oils fromcrude oils according to the prior art.

FIG. 2 is a block diagram illustrating three different general pathwaysand nine different general routes for creating base lube oils from usedlubricating oils according to the prior art.

FIG. 3 is a block diagram illustrating three different general pathwaysand seven different general routes for creating base lube oils fromcrude oils where the instant invention is noted as being implemented asthe last step in the processing scheme.

FIG. 4 is a block diagram illustrating three different general pathwaysand nine different general routes for creating base lube oils from usedlubricating oils where at least one embodiment of the present inventionis noted as being implemented as the last step in the processing schemeand only in the instance where the base oil has first receivedhydrotreatment.

FIG. 5 is a block diagram showing a preferred mode for implementing thesolvent extraction step on a hydroprocessed base oil processed through asolvent extraction column and with raffinate and extract streams shownhaving removal and recovery of solvent as well as generation of thehigher quality and lower quality product streams.

FIG. 6 presents a chart and table showing analytical results for thehigher and lower product quality streams were created when the processof at least one embodiment of the present invention was applied to avirgin hydroprocessed base oil (Purity 1003 fromHolly-Frontier/PetroCanada).

FIG. 7 presents a chart and table showing analytical results for thehigher and lower product quality streams were created when the processof at least one embodiment of the present invention was applied to avirgin hydroprocessed base oil (HCC 150 from Heritage Crystal Clean).

FIG. 8 is a block diagram showing how the raffinate (or extract) ispassed to a first solvent recovery column with residual passed to asecond solvent recovery column, which second solvent recovery columnpreferably also includes volatility and viscosity control functions.

DETAILED DESCRIPTION OF THE INVENTION

The following description is presented to enable any person skilled inthe art to make and use the invention, and is provided in the context ofa particular application and its requirements. Various modifications tothe disclosed embodiments will be readily apparent to those skilled inthe art, and the general principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the present invention. Thus, the present invention is notintended to be limited to the embodiments shown, but is to be accordedthe widest scope consistent with the principles and features disclosedherein.

Additionally, as used herein, the term “substantially” is to beconstrued as a term of approximation. Further, the term“hydroprocessing” is used herein to refer to hydrocracking,hydrotreatment, hydrofinishing, catalytic de-waxing, and iso-dewaxing aswell as any associated technologies which apply hydrogen and catalystsunder conditions of temperature, pressure, and residence times toachieve improvement in the feedstock. While streams and products createdby other hydroprocessing technologies may also provide suitablefeedstocks for the present disclosure, and the invention is thus notlimited to processing only hydrotreated base oils, a preferredhydroprocessing technology for creating feedstock for at least oneembodiment of the present invention is hydrotreatment (also referred toas hydrotreating).

Preferred process conditions for hydrotreating as contemplated in thepresent disclosure are preferably in the general ranges of 450° F. to700° F., and 600 psig to 1,500 psig. These process conditions preferablyresult in a loss of less than 10% of the lube fraction, and morepreferably result in a loss of less than 5% of the lube fraction, andmost preferably result in a loss of less than 2% of the lube fraction,with the lube fraction being defined as a range in which the majority ofthe liquid to be hydrotreated has boiling points from 550° F. to 1050°F. (these are atmospheric equivalent temperatures as this distillationwill occur under vacuum to avoid cracking). Hydrotreatment achievesimprovement in color, reduction in hetero-atoms (sulfur, nitrogen, andoxygen), and conversion of unsaturated components (such as aromatics) tosaturates (such as naphthenes). Many of the conversions from aromaticsto saturates create naphthenic components, and hydrotreatment also mayresult in naphthene ring opening and isomerization, thus converting somenaphthenes to paraffins, and some paraffins to iso-paraffins.

For purposes of applying specific solvents and process conditions, apreferable solvent is n-methyl-2-pyrollidone (nMP) although othersolvents may be utilized. Solvent to oil ratio ranges preferably include0.3 to 10.0, more preferably include 0.5 to 5.0, and most preferablyinclude 1.0 to 2.0, temperature ranges preferably include 25° C. to thelesser of the boiling point of the solvent (under the pressureconditions being applied), more preferably include 50° C. to 150° C. (orthe lesser of the boiling point of the solvent under the applicablepressure conditions), and most preferably include 60° C. to 90° C. (orthe lesser of the boiling point of the solvent under the applicablepressure conditions). Pressure conditions can range from vacuum (forexample as may be applied in the case of extractive distillation) toambient and beyond up to any pressure as may be applied to maintainintimate mixing of the solvent and the feedstock in a phase as bestpromotes the desired results of the applied process. The number oftheoretical stages of the extraction column preferably falls in therange of 1 to 10, more preferably in the range of 2 to 8, and mostpreferably in the range of 5 to 7.

In the present disclosure, solvent treatment is defined as applying oneor more solvents which will: (a) preferentially remove naphthenic,aromatic, polar, and/or waxy compounds from a hydrotreated base oil (asin the case of a solvent applied in solvent extraction) or (b)alternatively remove paraffinic compounds from a hydrotreated base oil(as in the case of a solvent removing paraffinic compounds as applied insolvent de-asphalting), or (c) use a combination of both (a) and (b)approaches. The combination of the two approaches described in (c) maybe any sequence of first (a) then (b), or first (b) then (a), or both(a) and (b) may be applied together simultaneously. In the case of (a)and (b) being applied simultaneously, then solvent treatment willpreferably include two solvents, namely a preferentially selectivenaphthenic/aromatic/polar/waxy solvent and a preferentially selectiveparaffinic solvent.

In the varied configurations noted above, the solvent or solvents arepreferably applied at different entry points to a contactor, extractor,centrifuge, extraction column (including a Scheibel Column),distillation column, or other device, which preferably promotesseparation of material by molecular weight and gravitational orcentrifugal force. Where a column is utilized then the preferred mode isto operate the solvent and oil countercurrently. Under the operatingconditions of the process, wherever two solvents (referred to herein as“dual solvents”) are employed such dual solvents will preferentially notbe miscible with each other but will instead preferentially haveincreased affinity for enhancing or detracting components which each iseither removing or acting as a replacement for, such as for exampleparaffinic components in the case of one solvent, andaromatic/polar/naphthenic/waxy components in the case of the othersolvent. In the case of dual solvents, temperature can have aparticularly significant impact wherein two solvents which aresubstantially immiscible at one temperature are substantially miscibleat another temperature. Whether practicing a single solvent or dualsolvents, in the present disclosure all solvents are preferablyrecovered from the product streams and re-used in the process. As usedherein, the terms “constituents”, “compounds”, and “components” are usedinterchangeably.

To illustrate one embodiment of how solvent extraction may beimplemented according to the present disclosure, in FIG. 5 thehydroprocessed base oil 500 is introduced and charged to solventextraction column 505 at connection point 504 which preferably occurs ina lower section of solvent extraction column 505. As a preferred mode ofthe invention a solvent (for example preferably nMP) is recycled backinto solvent extraction column 505 at connection point 503, whichpreferably is positioned in an upper section of solvent extractioncolumn 505. The solvent in this instance is heavier and thus it fallsdown through Solvent Extraction Column 505 passing counter-currently byHydroprocessed Base Oil 500 which, being lighter, is rising up SolventExtraction Column 505. As the solvent passes by and mixes withHydroprocessed Base Oil 500, the solvent preferentially attractsimpurities out of Hydroprocessed Base Oil 500, with such impuritiespreferentially being aromatics, naphthenic, and/or waxy components. TheHydroprocessed Base Oil 500, after rising to the top of the column, hashad its impurities substantially removed and then is called raffinate.In Raffinate 515, the solvent is distilled overhead and recovered andreturned via Solvent Recycle 520 for entry into Solvent ExtractionColumn 505 at connection point 503. Similarly, the solvent, afterdescending to the bottom of Solvent Extraction Column 505, then hascollected all the impurities and is then called extract. In Extract 530,the solvent is distilled overhead and recovered and returned via SolventRecycle 522 for entry into Solvent Extraction Column 505 at connectionpoint 503. Not shown is a small makeup of solvent over time as solventis passed out with the products. However, in a properly designed andconstructed unit, solvent losses are preferably extremely low (on theorder of parts per million). After the solvent is removed from theraffinate, the liquid that remains is passed as stream 540 and becomes ahigher product quality base oil 550. Similarly after the solvent isremoved from the extract, the liquid that remains is passed as stream535 and becomes lower product quality base oil 545.

Not shown in FIG. 5 are elaborate and often proprietary inner columnmechanical items which are designed to promote intimate contact betweensolvent and feedstock to maximize the performance of the extractionprocess. Also Raffinate 515 and Extract 530 may be one or moredistillation columns in series and also are preferably capable ofadditional functions beyond just solvent recovery as is described infurther detail below with respect to FIG. 8.

Turning to the results achieved by applying principles of the presentinvention (e.g. solvent treatment applied to processing a hydroprocessedbase oil) to processing multiple feedstocks, it was demonstrated quiteunexpectedly that a highly favorable improvement of the low temperatureproperties of the higher quality product was achieved and at yields inexcess of 80%. This favorable effect, and these favorable yields, wasachieved in both virgin and re-refined base oils. By volume, the higherquality product is the vast majority of the volume of the productsgenerated from each feedstock (about 85% in these experiments). Morespecifically, cold crank viscosities were reduced on average by about15% in a re-refined hydrotreated base oil and by about 13% in a virginhydrotreated base oil across temperature ranges of −25° C. to −35° C.Moreover, the improvement in the low temperature properties wasaccompanied by a favorable increase in the viscosity index in the rangesof 3 to 4 VI points (higher VI increases were achieved in alternativemodes of operating but this data is not reported) and without amaterially negative impact on volatility. With respect to the lowerquality product (which is about 15% yield of the feedstock), cold crankviscosities were increased, and thus it was degraded versus thefeedstock. However, even with higher cold crank viscosities, the lowerquality product remained a highly marketable base oil suitable for usein many applications. In addition, surprisingly favorable effects onpour point and cloud point in certain of the higher quality and thelower quality products were generally observed as well. Finally,indicatively oxidation stability in the higher product quality stream isincreased by removal of the less stable aromatic and naphtheniccompounds as a result of the solvent extraction process which createdthe higher VI product.

Although applying solvent extraction using n-methyl-2-pyrollidone tovirgin and re-refined hydroprocessed base oils in actual bench and pilotscale processes has demonstrated creation of substantially improvedhigher quality and lower quality streams, in the lower quality product,a haze or cloudiness was observed. This haze issue was addressed byfiltering, in which a vacuum pump was attached to a filtering flask andthe lower quality product was pulled (by the vacuum) into a receivingflask through Whatman filter paper inside a Buchner funnel. Followingthe filtration step, the lower quality product in the receiving flaskwas clear, without any haze or cloudiness.

Filtration processes are readily available at commercial scale so as toachieve a similar result as was achieved with the bench scale filtrationapparatus that removed the haze and cloudiness from the lower qualitystream. It may be that any favorable impact on the pour point and cloudpoint in the lower quality product noted above was enhanced by thefiltration step which removed the cloudy elements which appeared in thelower quality products after applying the solvent extraction step to thehydrotreated base oils. For example, these cloudy elements could be waxyelements that are then removed with a filtration step. The filter paperwas weighed before and after filtration and it showed a minimal increasein weight relative to the amount of the filtered product. So whateverwas removed was a very small portion of the lower quality productstream.

Table 3 shows the analytical results achieved by applying principles ofthe present invention to two feedstocks, the first a re-refinedhydrotreated base oil feedstock available from Heritage Crystal Cleancalled “HCC 150”, and the second a virgin hydrotreated base oilfeedstock available from PetroCanada (now owned by Holly-Frontier)called “Purity 1003”. Of notable interest is that even as the VIs of thehigher product quality are increased, the cold crank viscosities of thebase oils are decreased. Furthermore, in 3 of the 4 instances, there wasa material reduction in pour point, which is also favorable. Cloud pointalso was decreased slightly in 3 of the 4 instances. It was only thehigher quality re-refined HCC 150 product which did not exhibit adecrease in cloud point and pour point, although it did show the largestreduction in the cold crank viscosity of about 15% and a materialincrease of 3 points in VI. Also favorable is a slight reduction in theviscosity of both the higher and lower quality products. Since theprocessing temperature of each example in Table 3 was at least 225° C.below the temperature in which any cracking might be expected to evenstart, the slight reduction in viscosity is unexpected.

TABLE 3 Low Temperature Properties and Viscosity Index AnalyticalResults Re-refined (HCC 150) Virgin (Purity 1003) Feedstock Product AbsDelta % Delta Feedstock Product Abs Delta % Delta Test ASTM HigherQuality Product Yield = 85% Higher Quality Product Yield = 86% Viscosity@ 40 C. D-445 28.80 27.87 −0.93 −3.2% 21.60 20.47 −1.13 −5.2% Viscosity@ 100 C. D-445 5.30 5.24 −0.06 −1.1% 4.44 4.35 −0.09 −2.0% ViscosityIndex (VI) D-2270 118 121 3 2.5% 117 122 5 4.3% CCS @ −35 C. D-52938,302 7,036 −1,266 −15.2% 3,572 3,115 −457 −12.8% CCS @ −30 C. D-52934,175 3,569 −606 −14.5% 1,928 1,675 −253 −13.1% CCS @ −25 C. D-52932,253 1,930 −323 −14.3% 1,114 972 −142 −12.7% Pour Point D-97 −12 −12 0−15 −21 −6 Cloud Point D-2500 −5 −4 1 −8 −9 −1 Test ASTM Lower QualityProduct Yield = 15% Lower Quality Product Yield = 14% Viscosity @ 40 C.D-445 28.80 28.19 −0.61 −2.1% 21.60 21.18 −0.42 −1.9% Viscosity @ 100 C.D-445 5.30 5.11 −0.19 −3.6% 4.44 4.32 −0.12 −2.7% Viscosity Index (VI)D-2270 118 110 −8 −6.8% 117 111 −6 −5.1% CCS @ −35 C. D-5293 8,302 9,9591,657 20.0% 3,572 3,817 245 6.9% CCS @ −30 C. D-5293 4,175 4,886 71117.0% 1,928 2,036 108 5.6% CCS @ −25 C. D-5293 2,253 2,576 323 14.3%1,114 1,164 50 4.5% Pour Point D-97 −12 −21 −9 −15 −18 −3 Cloud PointD-2500 −5 −7 −2 −8 −12 −4

Of further interest is that as the cold crank viscosity of the higherquality product is decreased, so too is the cold crank viscosity of thelower product quality increased. FIGS. 6 and 7 (and the associatedtables therein) show key observations from the above Table 3 bothgraphically and numerically. In each of these charts, the feedstock isthe middle line, the line below is the higher quality base oil, and theline above is the lower quality base oil. For both feedstocks, over eachtemperature in the range of −35° C., −30° C., and −25° C., the higherquality product achieved materially improved CCS results. Further, ineach of the two products as the temperature of the CCS simulator test isreduced, the difference between the cold crank viscosities of the higherquality and lower quality products (as compared to the feedstock) isincreased. The results thus clearly demonstrate the positive effect onimproving the CCS of the higher product quality stream even as the CCSof the lower product quality stream is degraded.

Volatility is a measure of the extent of an oil to vaporize in use, witha common test method used to measure volatility being the NOACK ASTMtest D-5800. The NOACK test measures the amount of oil that hasvaporized when a sample is heated to 250° C. under a 20 mm vacuum,following a 1 hour period in which air is blown across the sample at afixed rate. In this apparatus, the higher volatility (light ends) areremoved from the starting sample and the difference in weight betweenthe starting and ending samples is the measure of volatility.

Since the products of implementing one embodiment of the presentinvention are both created from the same feedstock at relatively lowtemperatures (compared with the cracking ranges of the feedstock), nomaterial is being created (by means of cracking) or removed (in the formof non-condensable gases). Given this, arithmetically the amount ofvolatility gained by one product should be exactly offset by acommensurate loss in volatility in the other product (after adjustingfor yield differences). A hypothetical scenario that presents thisarithmetically is shown in Table 4. In Table 4, a 2.5% increase involatility in Product A (which is 40% of the output) is offset by a 1.7%reduction in Product B (which is 60% of the output). The increase in thevolatility of Product A is thus exactly offset by the decrease in thevolatility of Product B (after yield adjustment) so that the finalweighted volatility of the two products exactly equals the volatility ofthe feedstock.

TABLE 4 Arithmetic Calculation of Noack in 2 Products created from aHypothetical Feedstock Total Light Ends Noack Feedstock to SolventExtraction Step* 100 15 15.0% Product A 40 7 17.5% Product B 60 8 13.3%Back Blended Result 100 15 15.0% Mass Balance Crosscheck (must be 0 0 0equal to 0) *Feedstock separated into Product A and B where 100% of thefeedstock becomes either Product A or B. Assumes nothing is added to theprocess during the separation.

While the above analysis is supported by sound logic, in actual practicethe results of volatility testing on the products created by the twofeedstocks showed a slight increase in the volatility in all productscreated from each feedstock, an outcome which is theoretically notpossible. This is shown in Table 5 below.

TABLE 5 Volatility Results (Test Method, NOACK, D-5800) Products Noackdelta in Higher Quality Lower Quality Higher Lower Re-refined HCC 15012.3% 12.8% 15.7% 0.5% 3.4% Virgin Purity 1003 14.7% 15.4% 17.4% 0.7%2.7%

How this could happen is not understood. A possible minor contributormight be trace amounts of solvent still remaining in the products afterthe solvent was removed from the products via distillation. However,testing for solvent in products found at most about 1,900 ppm (0.19%) insome products (and usually it was much less). This means that the vastmajority of the volatility increase must be due to some other reason andfollow-up on the matter was justified.

Analytical testing of these products was done at the Southwest ResearchInstitute (SwRI), a world class testing facility in San Antonio, Tex.Testing at SwRI is applied scrupulously using the latest equipment(including regular testing against known standards) and lab techniciansare very experienced and diligent. SwRI confirmed that the approachoutlined in Table 4 above is theoretically sound, but that Noack'slimits of testing accuracy for repeatability is about 0.86% and forreproducibility is about 1.56% (in each case applied to the 12.3% Noackof the HCC 150 feedstock). So a possible contributor to the discrepancycould be the inherent limits in the accuracy of the test method. Analternative measure of volatility was offered which will be investigatedin the future.

Regardless as to the level of accuracy of the NOACK test method, inorder to further protect against higher volatility where a product mayexceed the 15% (or 13% or any other as specified to the application)level, an additional capability for volatility control as applied in thedistillation of the solvent is preferably included, and is nowdisclosed, as an element of one embodiment of the present invention.This is achieved by designing in further capability into a distillationcolumn which is used in the solvent recovery step after the extractionstep is first performed. By doing this, volatility of the higher orlower quality products can be adjusted by removing a small portion ofthe light base oils and a small portion of the heavier portion of thissame light base oil. Furthermore, if products have viscosities that falloutside the range required for a specific market application, then theviscosities can be adjusted by designing the distillation column notonly for removal (and recovery) of solvent (and volatility control), butalso for fractionation into viscosities as are suited for the specificmarket application. By doing this, multiple products can be createdusing a column that would otherwise be used solely for solvent recovery.By incorporating the ability to adjust at least one of volatility andviscosity of the products into a solvent recovery section, capital costand operating cost savings may be achieved. For example, modifying atraditional design for a column that is used solely for solvent recoverywill reduce the capital cost of adding a further column solely forproduct viscosity or volatility adjustment. Furthermore, using this samecolumn will preferably be implemented to achieve lower operating cost bymaintaining some or all of the higher temperatures and reduced pressuresas are used for recovery of solvent. Even if a subsequent column is usedafter a first solvent recovery column, operating cost savings arepreferably gained by maintaining some or all of the higher temperaturesand reduced pressures as are used in the last distillation column whichis recovering the solvent.

To convey this further element graphically, FIG. 8 illustrates araffinate (which could separately be an extract stream) stream 800 beingcharged to a distillation column 810 for purposes of recovery of some ofthe solvent in stream 840. The material not proceeding overhead 835(this is the raffinate stream with some of the solvent removed) is thencharged to a second distillation column 820 whereupon virtually allremaining solvent is removed and recovered in stream 845. The nextheavier fraction depicted in the second distillation column 820 is aSpindle Oil stream 850 as a side draw, as is the next heaver fractionbeing a Light Base Oil 855. The residual is shown as a Medium or HeavyBase oil stream 860. To achieve volatility control, the column isdesigned to remove the lighter ends from the Light Base Oil 855 (whichthen becomes part of the Spindle Oil 850) and to ensure the viscositytarget is still met, a portion of the heavier liquid contained in LightBase Oil 855 is instead portioned into Medium or Heavy Base Oil 860(thus increasing the yield of the Medium or Heavy Base Oil).

Careful management of the material to be removed from each fractionenables achievement of target viscosities even as the volatility ismanaged to fall within the required specification. But to place all thisin proper context, and as is well known in the industry, in lighter lubeoils to achieve both low volatility and low viscosity without exceedingvolatility requirements requires a higher VI feed stream, which is thusassumed to preferably be the higher VI raffinate stream used in theabove description. Alternatively stated, one cannot simply applyfractional distillation to create a low viscosity, low volatilityfeedstock without that feedstock being of a sufficiently high productquality from the start. It is thus apparent that, to make lighterviscosity lubricants, at least one process of the present invention mustimprove the VI of the raffinate to a sufficient degree that thevolatility control and viscosity fractionation functions can then bepreferentially and beneficially applied; in this way the solventtreatment and fractionation processes of at least one embodiment of thepresent invention are dependent upon each other.

The above noted fractionation step can have certain variations, some ofwhich are described next. While the above design presents two columns inseries, in some instances it may be preferable to design the process fora single column processing stream 800. In addition, the furthervolatility control and viscosity fractionation functions (which are inaddition to solvent recovery) described above may be included forprocessing of either or both of the higher and lower product streamsshould volatility or viscosity control be desired in either of theraffinate or extract streams. Furthermore, in FIG. 8, the productspresented are a spindle oil, light base oil, and medium base oil, butthe creation of fewer or more products can be designed as alternateconfigurations to suit specific market requirements. In any event, byimplementing the above fractionation step (or using a similar approach),each of solvent recovery, volatility control, and viscosity targetingfor specific market applications may all be afforded at reduced capitaland operating costs. Proper design of fractional distillation columns iswell known and functional design elements needed to achieve not onlysolvent recovery but also volatility and viscosity control, areachievable as described above if engineered by one of ordinary skill inthe art.

As noted above, a particularly unexpected outcome of practicing at leastone embodiment of the invention was achieving both a large improvementin low temperature properties of the higher quality product relative tothat of the feedstock and a simultaneous improvement in the ViscosityIndex (VI) in the higher quality product, also relative to that of thefeedstock. The result is unexpected because it is known that higherparaffinic content will result in an increased VI and it was furtherassumed, since the hydrotreated base oils were almost fully saturated,that the VI improvement being achieved could only occur by reducing theproportion of naphthenes in the higher quality product, there presumablybeing very little (if any) aromatics left in the feedstock to remove.However, it is also known that naphthenes exhibit better low temperatureproperties than paraffins. Therefore a reduction in naphthenes in thehigher quality product would logically be assumed to have resulted indegraded (versus improved) low temperature properties (such as the coldcrank simulator results) in the higher quality product. But that did notin fact happen. A posed theory as to how both VI and low temperatureproperties could simultaneously be improved is that some residual waxycomponents in the feedstock were removed from the raffinate by thesolvent treatment (and then appeared as haze in the extract), thusleaving fewer waxy elements in the higher quality product. But verylittle waxy material was recovered in the filtration process, indicatingthat if this is actually the explanation for the improved cold crankviscosity, not much removal is needed to achieve highly beneficial lowtemperature results. A further item to be reconciled is that waxycompounds are known to increase VI, and so if their removal caused abetter result in the cold crank viscosity in the higher quality streamthat should also have been accompanied by a worst result in the VI ofthe higher product quality stream. But that too did not happen. Furtherinvestigation into why solvent extraction of hydrotreated base oilcreated both improved low temperature properties and higher VI in thehigher quality products requires compositional analysis of theproportions of paraffins (including n and iso-paraffins), naphthenes(including more particularly proportional content by number of rings),residual wax components, as well as any aromatics (or non-technicallydescribed, any quasi-aromatic-naphthenes) that may be drawn into thelower quality product through the solvent treatment step appliedaccording to principles of the present disclosure.

As discussed in the background of this specification, a major goal oflubricant improvements is to extend and maximize the useful life of thelubricant, thus delaying a need for its replacement in the application.Not only does a longer lubricant life represent cost savings from lessfrequent changes, but it also indicates a higher average level ofperformance versus time, thus providing better lubrication even while alubricant is being degraded during use. To achieve a longer duration ofthe lubricant, it must have strong oxidation stability and this ismeasured and is thus an additional important property of base oils. Ingeneral, aromatic and naphthenic compounds are less stable and moreprone to break down, leading to sludge formation and deposit creationand impaired lubricating capability as the lubricant is degraded fromuse. Since an effect of solvent treatment is separation of aromatic andnaphthenic compounds out of the feedstream to create the higher productquality product, improved oxidation stability of the higher qualityproduct is indicatively achieved by applying principles of the presentdisclosure. Therefore, in addition to the noted improvements in both thelow temperature properties and Viscosity Index of the higher productquality stream, compositional improvement in the higher product qualitystream of one embodiment of the present invention forecast improvementin the oxidation stability of the higher product quality stream.

The present invention is not limited to any particular solvent in thesolvent treatment process, or catalyst in the hydroprocessing steps,since feedstocks and process conditions may vary and principles of thepresent invention may be applied in many varied modes. Solvents are alsoknown for selectively separating aromatics, polars, and otherundesirable base lube oil constituents from desirable base lube oilconstituents. Preferred solvents typically compriseN-methyl-2-pyrollidone, furfural, phenol, and the like. The optimumsolvent may be selected based upon its effectiveness in the process asdiscussed above, but an alternate approach may be to utilize othersolvents known for their preferential selectivity for removingparaffinic components. Such preferred solvents typically comprisepropane, acetone, hexane, heptane, isopropyl alcohol, and the like. Theoptimum solvent may be selected based upon its effectiveness in thesolvent treatment process as it may be applied as described according toprinciples of the present invention or in any alternate embodiment.

While the present invention has been described by reference to certainof its preferred embodiments, the embodiments presented here areintended to be illustrative rather than limiting in nature and manyvariations and modifications are possible within the scope of thepresent invention. Many such variations may be considered obvious anddesirable by those skilled in the art based upon a review of theforegoing description of the preferred embodiments that are described inthis specification.

1. A method comprising the step of applying to a hydrotreated base oil a solvent treatment comprising at least one solvent to produce at least one first base oil, and one or more additional base oils, wherein the at least one first base oil has a higher paraffinic content than occurred in the hydrotreated base oil.
 2. The method of claim 1 wherein the hydrotreated base oil feedstock is derived from one of a crude oil feedstock and a used lubricating oil feedstock.
 3. The method of claim 1 wherein the hydrotreated base oil has been hydrotreated under a pressure of at least 600 psig.
 4. The method of claim 1, further comprising a step of utilizing in the solvent treatment at least one of a preferentially selective paraffinic solvent, and at least one of a preferentially selective solvent for at least one of aromatic, polar, and naphthenic constituents.
 5. A method for controlling at least one of volatility and viscosity of a base oil product by applying to a hydrotreated base oil feedstock a solvent treatment in which a first base oil is created that has a VI that is greater than that of the hydrotreated base oil feedstock and a further fractionation step comprising no less than two of: a. removal of solvent from the raffinate from which the first base oil was made, b. volatility of the first base oil that is at least one of (1) less than or equal to 15% or (2) less than or equal to 13%, in each case as measured by ASTM D-5800, and c. viscosity of the first base oil that is less than that of the hydrotreated base oil feedstock.
 6. The method of claim 5 wherein the hydrotreated base oil feedstock is derived from one of a crude oil feedstock and a used lubricating oil feedstock.
 7. The method of claim 5 wherein the hydrotreated base oil contains at least 90% saturates.
 8. The method of claim 5 wherein the hydrotreated base oil contains less than 300 PPM of sulfur.
 9. The method of claim 5 wherein the hydrotreated base oil has been hydrotreated under a pressure of at least 600 psig.
 10. A method comprising a step of applying to a hydrotreated base oil feedstock a solvent treatment in which a first base oil is created that has an improved result, whenever tested either as a base oil or as a component of a finished lubricant, in at least one of the following ASTM tests relative to that of the hydrotreated base oil feedstock. a. Wear and Oil Thickening (D-7320), b. Wear, Sludge, and Varnish Test (D-6593), c. High Temperature Deposits, TEOST MHT (D-7097), d. High Temperature Deposits TEOST 33C (D-6335), e. Aged Oil Low Temperature Viscosity, ROBO Test (D-7528) f. Aged Oil Temperature Low Temperature Viscosity (D-7320). g. Determination of Oxidation Stability of Straight Mineral Oils (IP-306), h. Test of Susceptibility of Ageing According to Baader (DIN 51554), i. Oxidation Characteristics of Inhibited Mineral Oils (D-943), j. Determination of the Sludging and Corrosion Tendencies of Inhibited Mineral Oils (D-4310), k. Oxidation Stability of Steam Turbine Oils by Rotating Pressure Vessel Oxidation Test (RPVOT), (D-2272), l. Determination of oxidation stability and insolubles formation of uninhibited turbine oils at 120° C. without the inclusion of water (Dry TOST Method) (D-7873), m. Determination of Oxidation Stability of Inhibited Mineral Turbine Oils (IP-280), n. 3462 Panel Coker Test (FTM 791A), o. Standard Test Method for Corrosiveness and Oxidation Stability of Hydraulic Oils, Aircraft Turbine Engine Lubricants and Other Highly Refined Oils (D-4636), p. Pneurop Oxidation (DIN 51352), q. Standard Test Method for Thermal Stability of Hydraulic Oils (D-2070), r. Hydrolytic Stability of Hydraulic Fluids (Beverage Bottle Method) (D-2619), or s. Oxidation Characteristics of Extreme Pressure Lubricating Oils (D-2893)
 11. The method of claim 10 wherein the hydrotreated base oil feedstock is derived from one of a crude oil feedstock and a used lubricating oil feedstock.
 12. The method of claim 10 wherein the hydrotreated base oil contains at least 90% saturates.
 13. The method of claim 10 wherein the first base oil has a viscosity index of at least
 120. 14. The method of claim 10 wherein the hydrotreated base oil has been hydrotreated under a pressure of at least 600 psig.
 15. A method comprising the step of applying to a hydrotreated base oil a solvent treatment comprising at least one solvent to create at least one product stream with an improvement in at least two of: a. viscosity index, b. volatility, and c. at least one of cold crank viscosity, Brookfield viscosity, pour point, and cloud point, relative to that of the feedstock.
 16. The method of claim 15 wherein the hydrotreated base oil feedstock is derived from one of a crude oil feedstock and a used lubricating oil feedstock.
 17. The method of claim 15 wherein the hydrotreated base oil contains at least 90% saturates.
 18. The method of claim 15 wherein the hydrotreated base oil contains less than 300 PPM of sulfur.
 19. The method of claim 15 wherein the first base oil has a viscosity index of at least
 120. 20. The method of claim 15 wherein the hydrotreated base oil has been hydrotreated under a pressure of at least 600 psig.
 21. The method of claim 15 wherein the hydrotreated base oil is hydrotreated at a pressure less than 1500 psig and a temperature less than 650° F. 